Contactors including sockets, probes, spring pins and interposers are routinely used in systems for: (a) testing electronic device performance (an assortment of socket types has been developed to connect to a device under test (“DUT”) having a wide variety of terminals and configurations), or (b) burning-in electronic devices at elevated temperatures. Miniature contactors are used widely in such sockets to make contact to terminals on microelectronic devices. For example, a socket used for test or burn-in applications will typically have contactors with mechanical compliance that accommodates imperfections in a DUT as well as warping and non-planarity of a printed circuit board to which the socket is attached.
Prior art sockets are differentiated typically according to the type of terminals on a DUT, and according to an intended end use (i.e., application). For example, contactors used in sockets are typically designed to make electrical connection to terminals on microelectronic devices wherein the types of device terminals contacted by sockets include pin grid arrays (“PGAs”), J-leads, gull-wing leads, dual in-line (“DIP”) leads, ball grid arrays (“BGAs” such as, for example, a two dimensional array of solder bump terminals on a microelectronic device), column grid arrays (“CGAs”), flat metal pads (sometimes referred to as land grid arrays (“LGAs”)), and many others. Many contactor technologies have been developed to provide sockets for microelectronic devices having this variety of terminals.
In addition to the foregoing, further differentiation among prior art sockets refers to low insertion force (“LIF”) sockets, zero insertion force (“ZIF”) sockets, auto-load sockets, burn-in sockets, high performance test sockets, and production sockets (i.e., sockets for use in products). In further addition to the foregoing, low cost prior art sockets for burn-in and product applications typically incorporate contactors of stamped and formed springs to contact terminals on a DUT. In still further addition to the foregoing, for high pin-count prior art sockets, a cam is often used to urge device terminals laterally against corresponding contactors to make good contact to each spring while allowing a low or zero insertion force.
For specialized applications, prior art sockets have used a wide variety of contactors, including anisotropic conductive sheets, metal filled elastomeric buttons, flat springs, lithographically formed springs, fuzz buttons (available from Cinch, Inc. of Lombard, Ill.), spring wires, buckling beams, barrel connectors, and spring forks, among others. Prior art sockets intended for applications where many test mating cycles (also referred to as socket mount-demount cycles) are required typically use spring pin contactors of the type exemplified by Pogo® spring contacts (available from Everett Charles Technologies of Pomona, Calif.).
Spring probes for applications in the electronics test industry are available in many configurations, including simple pins and coaxially grounded pins. Most prior art spring probes consist of a coil spring disposed between a first post (for contacting terminals on the DUT) and a second post (for contacting contacts on a circuit board—a device under test board or “DUT board”). Spring probes are designed typically to undergo about 500,000 insertions before failure.
Spring probe contactors of the prior art provide reliable, high performance contact to terminals on many types of microelectronic device. A continuing increase in areal density of terminals has driven terminal spacing down below 0.4 mm, thereby increasing the cost and complexity of spring probe contactors. In particular, spring probes are typically made by a manual procedure wherein: (a) a miniature post is inserted into a sleeve; and (b) a spring and a second post are then inserted and crimped in place. This manual procedure becomes more difficult and expensive for the small contactors required for terminal spacing below 0.4 mm. Further, attempts to simplify spring probes by using only a coil spring as the contactor have largely failed. In a spring pin of the Pogo® type, the moving post must make good contact with the conductive sleeve to avoid signal current's passing through the coil and producing undesirable inductance and resistance. A coil spring at such small dimensions has too high an electrical resistance and inductance to be useful for any but the least demanding socket applications.
Spring probe contactors typically have a plurality of spring pin contactors disposed in an array of apertures formed through a dielectric holder. By way of example, a high performance, prior art test socket may incorporate a plurality of Pogo® spring contacts, each of which is held in a pin holder with an array of holes through a thin dielectric plate. The dielectric material in a high performance, prior art test socket is typically selected from a group of dimensionally stable polymer materials including: glass reinforced Torlon 5530 (available from Quadrant Engineering Plastic Products, Inc. of Reading, Pa.); Vespel; Ultem 2000 (available from GE Company GE Plastics of Pittsfield, Mass.); polyether ether ketone (PEEK); liquid crystal polymer; and others. The individual Pogo® spring contacts are typically selected and designed for signal conduction at an impedance level of approximately fifty (50) ohms.
The recent growth in use of BGA terminals for integrated circuit (“IC”) packaging has resulted in use of new and varied sockets adapted to the BGA terminals for increasing terminal count and area density. BGA sockets have evolved in several directions. One type involves use of a cam driven spring wire to contact the side of each ball on a BGA package. Another type involves use of spring pins or Pogo® spring contacts that have been adapted for use in BGA sockets for certain applications in which the high cost of the socket is acceptable.
Low-cost sockets for mass market applications have evolved the use of stamped and formed spring contactors that cradle each ball of the BGA and provide some measure of mechanical compliance needed to urge a spring connector into contact with a mating ball. Variations of stamped and formed springs are configured to use two or more formed springs to grip each ball, and thereby, to make positive electrical contact while retaining the ball mechanically. Miniaturization and density of mechanically stamped and formed springs are limited by present capabilities to a certain minimum size. As such, sockets with such contactors are limited in density by the complexity of stamping and forming very small miniaturized springs. Further, the mechanical compliance of a stamped and formed spring is typically small in a vertical direction perpendicular to a substrate of a ball contact. Because of small compliance in a vertical direction, a miniature stamped and formed spring may be unable to accommodate motion of a contactor support relative to a ball mated to it, thereby allowing vibration, mechanical shock load and forces, flexure, and the like to cause the connector to slide over the surface of the ball and potentially lose contact.
Many prior art sockets are intended to provide reliable and repeatable electrical contact to electrical terminals without causing damage to either. As such, the contactors of the socket must provide a low resistance connection to mating terminals over repeated insertions of devices. A continuing increase in the areal density of terminals on high performance microelectronic devices increases the difficulty and cost of providing reliable contactors.